The long range goal of this project is to develop an understanding of the dynamics of DNA in solution and to determine how the dynamics affect the structure and function DNA. Ultraviolet radiation can convert adjacent pyrimidine bases in DNA into cyclobutane dimers. Local denaturation of the helix results from the breaking of hydrogen bonds and the disruption of base stacking. The dimers have been implicated as biological lesions. The mechanism for their recognition and repair is poorly understood. Therefore the technique of transient electric birefringence will be used to determine the rotational and internal bending dynamics of DNA fragments of known sequence with thymine dimers located in-phase on the helix. The results will be compared with the same fragments without the dimer. A comparison of these results will permit a very accurate determination of the bend angle that is probably introduced into DNA. Bent or curved DNA, which arises from phased poly(dA).poly(dT) tracts, is found in kinetoplasts and at the origin of replication. Its function is not entirely understood. The nature of the bending is unclear and may arise from dynamics will be used to study the relaxation spectra of DNA fragments to distinguish between these mechanisms. Since the affinity of repressors for operators influences regulation and since the interaction of repressors with operator sequences requires distortion of the DNA structure, the elastic distortion of the DNA structure may play a pivotal role in the regulatory process. Therefore the sequence dependence of the flexibility and the internal bending dynamics of DNA will be studied using the technique of transient electric birefringence.